[PR64817-related 3/3] simplify xor of (and or ior) of xor

[Jakub Jelinek]

On Wed, Feb 04, 2015 at 04:21:43AM -0200, Alexandre Oliva wrote:
> I'm a bit surprised the gimple layer does not even attempt to simplify
> them, but I didn't try to tackle that, since I was not even sure this
> was a useful optimization.  After all, how often do we see xor of and of
> xor of and of xor of... in the wild, rather than in pathological
> testcases? :-)  But hey, at least the rtl simplification is cheap, so
> why not?

I think we should teach at least VRP to simplify debug stmts similarly how
it simplifies normal comparisons etc. using value ranges, but that would be
stage1 material.

> Regstrapped on x86_64-linux-gnu and i686-pc-linux-gnu.  Ok to install?
> 
> for  gcc/ChangeLog
> 
> 	* simplify-rtx.c (simplify_binary_operation_1): Simplify one
> 	of two XORs that have an intervening AND or IOR.

Ok, thanks.

	Jakub